As a plug-in type optical connector, namely a backplane connector is known. With the backplane connector, by inserting a printed board in a plug-in unit, an optical connector attached to a backplane of the plug-in unit, and an optical connector attached to the printed board are connected. For example, in Patent Literatures 1 and 2, such a backplane connector is disclosed. Patent Literature 1 discloses a coupling mechanism of an optical connector having an outer housing and an inner housing. Patent Literature 2 discloses that by making the optical connector to the backplane side float in respect to the backplane, misalignment when fitting the optical connectors to each other can be absorbed.